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Impact of Deformations and Posture Variations On Surface-Guided Radiation Therapy of the Breast

J Meyer*, L Wootton , University of Washington, Seattle, WA


(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 5

Purpose: To characterize and quantify the behavior of a commercial surface-guided radiation therapy (SGRT) system in the presence of translations, rotations, anatomical deformations and posture variations.

Methods: The C-RAD Catalyst SGRT system uses a deformable surface registration algorithm to compare a reference surface with a live surface. Shift parameters are calculated to correct for setup uncertainties relative to isocenter. Transformations to the reference surface were investigated for a rigid female torso phantom setup. Rotations (±4°) and deformations related to breast size (±2 cm), arching/hunching back (±4 cm), distended/deflated abdomen (±5 cm) and a blanket covering the lower abdomen (+2 cm) were introduced in software. The C-RAD calculated corrections were assessed for different isocenter locations, including in the breast and supraclavicular (SCV) region, in combination with the different deformations.

Results: The C-RAD calculated shifts for rigid transformations were all within 1 mm and 1° of the expected values. For yaw and pitch rotations, the difference in calculated shifts between the breast and SCV isocenters was >2 mm/1° in lateral and vertical direction, respectively. Breast size changes resulted in non-linear vertical shifts up to a maximum of 9 mm. The largest differences between the two isocenters were obtained for a hunching/arching back with up to 16 mm and 7° in the calculated shifts.

Conclusion: The C-RAD performance for rigid transformations was consistent and within the system’s measurement accuracy. Rotational setup errors resulted in different shifts depending on isocenter location. This is due to geometrical factors and therefore algorithm independent. The same anatomical deformations and posture variations can result in relatively large differences in shift parameters for different isocenter locations. When field matching is required, great care should be taken to minimize rotations and deformations relative to the reference surface prior to treatment to avoid gaps/overlap in the field junction region.


Deformation, Surface Matching, Breast


TH- RT Interfraction motion management : setup errors, immobilization, localization

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